Apparatus for granulation of very small particles is now commonplace in industry. It is used, for example, in the preparation of "instantized" drinks and in the detergents industry for formation of special components such as enzyme granules, anti-foam granules or bleach components. In the detergents industry one of the most popular apparatus is a drum granulator, since in this type of apparatus it is easiest to arrange for the high throughput desired to be achieved with employment of minimum labour. Additionally, movement of material through a rotating drum is virtually plug flow, so it is easy to arrange sequential addition of coating materials so that layered granules can be built up. Rotating drums can also be used for simple mixing processes.
One of the difficulties with drum granulators is that in the process of granulating fine particles a sticky mass of powder may be formed which tends to adhere to the drum wall and has to be scraped off. However, in certain applications it is desirable to lift the powdered feed material to the top of the drum, in which case internal baffles are needed. In this case scraping of the wall is not possible and thick layers of wetted material will build up on the drum wall.
This disadvantage is overcome in the present invention by forming the drum wall from a resiliently flexible material and rotating the drum past an obstruction which deforms the wall.